Random Read & Write Patterns

Now we’ll see the dependence between the drives’ performance in random read and write modes on the size of the data block size.

We will discuss the results of the disk subsystems at processing random-address data in two versions. For small-size data chunks we will draw graphs showing the dependence of the amount of operations per second on the data chunk size. For large chunks we will compare performance depending on data-transfer rate in megabytes per second. This approach helps us evaluate the disk subsystem’s performance in two typical scenarios: working with small data chunks is typical for databases. The amount of operations per second is more important than sheer speed then. Working with large data blocks is nearly the same as working with small files, and the traditional measurement of speed in megabytes per second becomes more relevant.

There are three groups of drives in the random read test. The leading group includes the Blue and the Black models from Western Digital. Judging by the similar results, the actuators of these two models are equally quick. The Seagate and Samsung with similar performance are in the second group. The 5400rpm Green model from Western Digital takes last place. The nice-looking neat graphs are only spoiled by the sudden slump of the Seagate on 128KB data blocks, reminding us of the slump in its sequential reading graph. This effect seems to occur on 128KB data blocks rather than after them.

All of the drives, save for the WD Caviar Green, go close to each other. The Samsung is just a little slower than the others, probably because of its lower sequential read speed. The data blocks are large here, after all.

When writing in small data blocks, we can see the consequence of the Seagate Barracuda 7200.11 having shown a poor write response time. It processor seems to be unable to cope with the numerous small-size random-address data chunks while doing deferred writing. That’s sad because Windows processes system registry and many other system data in 512-byte blocks. As for the other HDDs, the Samsung is noticeably faster than the pair of Western Digital drives which have identical results again. The Black model doesn’t show its superiority as yet.